The present invention relates to a watch movement part comprising a frame bearing a striking work mechanism which comprises a motor member kinematically linked with a striking work wheel, a striking work member mounted to pivot on the frame and comprising an anchor attached to a striking work hammer, this anchor having two pallets engaged alternately with said striking work wheel to make said striking work hammer oscillate between a first position striking a resonant member and a second position defined by a limiting member.
The frequency of oscillation of the striking work hammer must be low enough for the sound to be able to be diffused when the gong of the striking work enters into resonance, but also to maximize the duration of the ringing.
A conventional striking work mechanism consists of a barrel engaged with a gearwheel attached to a striking work wheel designed to drive the striking work hammer. This hammer is cinematically attached to an anchor, the two noses or pallets of which slide alternately over the inclined flanks of the teeth of the striking work wheel when the latter is driven in rotation by the barrel, so that the hammer oscillates between a position in which it strikes the resonant member of the striking work and a second position defined by an abutment.
The frequency of oscillation of the hammer depends on the torque of the motor spring, on the inertia of the hammer, and on the tolerances of assembly of the different components. The slightest variation of one of these parameters affects the hammer strike rate and therefore the sound quality and the duration of the ringing. However, the dimensional tolerances, and those of assembly do not make it possible to obtain a repeatable strike rate, and there is no means for adjusting it.
Moreover, the weight of the hammer is chosen such that, in a given bulk, its inertia is as great as possible. This has the advantage, for a given motor torque, of obtaining a low strike frequency which allows for a better diffusion of the sound of the gong of the striking work. However, in this case, the strike rate of the hammer, and therefore the duration of the ringing and the quality of the sound, are all the more sensitive to the effect of gravity, and therefore to the orientation of the wristwatch.
Finally, this design induces, in the event of an impulse of the hammer towards the limiting abutment, two distinct shocks of the strike itself. The first shock originates from the impact of the hammer against this abutment and the second shock is provoked by the contact between the anchor and one of the teeth of the striking work wheel, which has the effect of producing a jerky ring accompanied by a spurious noise. One solution would be to eliminate the limiting abutment so that the hammer abuts against one of the teeth of the striking work wheel, but this design does not eliminate the spurious noise and risks producing premature wear of the striking work mechanism.
CH 431 393 has proposed a striking work mechanism which makes it possible to obtain either an automatic variation of the strike rate of the hammer during ringing, or a ringing with continuous rate. This mechanism has only two positions and it does not therefore allow an accurate adjustment of the strike frequency of the striking work hammer. It is, moreover, complicated and comprises a large number of parts. Furthermore, since the anchor is separate from the hammer, the chain of tolerances is thereby particularly important, resulting in a wide dispersion of the strike frequency of the striking work hammer.
CH 700 606 describes another striking work device in which the pivoting axis of the hammer passes through its center of gravity so as to render the mechanism less dependent on the orientation of the watch. This striking work mechanism does not, however, allow the strike frequency of the hammer to be adjusted, nor does it make it possible to reduce the spurious noise of the mechanism and the premature wear of the striking work mechanism.
To mitigate the shock between the hammer and the abutment which limits its displacement, the Vulcain V10-H2 Golden Voice movement includes an O-ring seal on the abutment which serves as a damping element. However, such a seal does not cancel the risk of having spurious noises appear. Also, the latter does not make it possible to adjust the strike rate of the striking work hammer.